TYPES OF BIKE HYDRAULIC BRAKES, THEIR ADJUSTMENT AND BLEEDING
Hydraulic brakes are used primarily on bicycles where precision, responsiveness and reliability are required. First of all, these are heavy, massive mountain bikes designed to overcome steep slopes and climbs. Also, hydraulics have become an integral part of high-speed bicycles, as it allows you to very accurately and in the shortest possible time reduce speed.
The principle of operation of hydraulic brakes is very similar to mechanical brakes, where the brake pads are operated by a cable. The only difference is that in the hydraulics, instead of cables, brake fluid is used, and levers and eccentrics replace the cylinder-piston groups. Thanks to this approach, the frictional forces in the system are significantly reduced, and this increases its service life.
Despite this, hydraulics also has disadvantages, first of all, it is difficult to repair in case of breakdown. For example, in the event of a breakdown in the hydraulic line, the brakes cannot be repaired in the field. The most that is possible with the tools is to bleed the hydraulic brakes.
BY TYPE OF CALIPER FIXING
The caliper attaches to the frame or fork in different standards, depending on which standard the manufacturer decides to use on its products. Also, the mount is influenced by the attachment point (front or rear wheel) and the size of the rotor, depending on which it is necessary to mount the caliper at a certain distance from the center of the wheel. For the interaction of all these standards with each other, special fastening adapters (adapters) are used.
- (PM). Post Mount. now the most common standard used on most modern bicycles;
- (IS). International Standart. outdated mounting option. If it is used somewhere, then it will most likely be the so-called Ashanbays;
- (FM). Flat Mount. A rare standard commonly found in road and cyclocross bikes.
BY NUMBER OF PISTONS
Finally, the most expensive design variation is the number of pistons. A variation that relates directly to the hydraulic circuit and changes the entire force distribution system.
There are several of them for hydraulic brakes:
- 2 pistons. one on both sides of the rotor. The classic most common option. Used on most bicycles and most cycling disciplines. Covers categories from the lowest-cost to the top-end systems. The power of the two pistons is usually enough head-to-head for most riders;
- 4 pistons. two on each side of the rotor. The choice for those looking for exceptional braking power. They are used mainly in extreme types of disciplines: downhill, enduro, freeride. In addition to excellent braking properties, it is also important here that more efficient heat dissipation occurs in this configuration. And this is an important nuance for those who like extreme descents, when both the rotor and the caliper get so hot that ordinary brakes lose efficiency and the brake lever can simply start to fail without compressing the pads;
- 6 pistons are an extremely rare design and are mainly produced by the Chinese brothers. In addition to the frightening appearance, it has no other advantages.
BY ROTOR MOUNTING TYPE
There are several standards for attaching a rotor to a bicycle wheel hub. Although rotors are not part of a hydraulic brake, but without them, you can not anywhere, and when choosing brakes, most likely you will come across this question:
- Centerlock is a Shimano brand standard. At the same time, Shimano produces both hubs and rotors for 6 holes;
- Six holes (6-hole). Sram brand standard. At the same time, Sram produces both bushings and rotors for a central block;
- 4.5 holes. An extremely rare option, but there are such.
Bleeding hydraulic brakes
When the entire system has already been completely sorted out and assembled, it remains only to fill in the brake fluid and properly pump the hydraulics. The system is pumped in order to expel air bubbles from all pipes and cylinders, which prevent the hydraulics from working correctly.
There are a lot of ways how the hydraulic brakes of a bicycle are pumped. Anyone can do this at home, if they know how to handle tools a little. Someone uses syringes, and someone uses old and proven methods. Consider the simplest and most time-tested option.
To bleed the brakes, you will need the following components:
- a transparent tube, suitable in diameter to the bleed bolt;
- brake fluid or oil, depending on the specific system;
- required keys;
- jar or bottle;
- a piece of clean cloth to keep it clean.
First you need to put a transparent hose on the bleeding bolt, and lower its other end into a jar, where there should be some brake fluid. Next, you need to open the brake fluid reservoir on the handle and make sure that it is at the maximum level. If necessary, the liquid must be topped up.
Attention! The brake fluid is unique for each bike model and cannot be mixed or replaced.
The better (and easier) way to bleed Shimano brakes | Syd Fixes Bikes
After that, you can start bleeding the disc brakes on your bike. Pressing the brake lever several times, you need to fix it in the pressed state and at the same time unscrew the screw for bleeding on the brake machine. In this case, you can observe how air bubbles will go out of the tube. After that, the screw must be tightened immediately, and only then you can release the handle and swing again.
This procedure must be repeated several times until the whole system works as it should. This can be felt by the stiffness of the brake lever.
Video showing the pumping procedure:
And one more way to pump the hydraulic line for the lazy:
DIFFERENCES OF HYDRAULIC BRAKES
Let’s consider how hydraulic brakes differ from each other from different manufacturers and for different bicycles.
BY BRAKE FLUID TYPE
Mineral oil is the most common type of brake fluid. Not dangerous for paintwork and plastic parts of the bicycle, which can easily get on when bleeding the brake system. Used by brands such as: Shimano, Magura, Campagnolo, TRP, Formula and others;
Dot (DOT 5.1, DOT 4.1). This type of brake fluid is used mainly by the Hope and Sram brands. It has a different chemical composition and slightly differs in properties from mineral oil. caustic substance. Therefore, when pumping the brake system, it is necessary to ensure that the pillbox does not fall on the elements of the bicycle. And if it does, then try to remove it as quickly as possible with a rag from the paintwork and plastic elements of the bike.
Which hydraulic brake bleed kit is best?
So that the system can be serviced at home, bicycle parts manufacturers produce special kits that contain all the necessary components. The standard set consists of:
- a syringe for filling and purging brake fluid;
- tubes (one or more);
- funnel for filling oil;
The complete set may vary for different manufacturers, there are kits that immediately include mineral oil, additional crimping rings, clamps and other useful devices.
If you have doubts about the ability to independently service the hydraulics, it is better to entrust this work to the specialists in the bicycle workshop. They will be able to carry out diagnostics and high-quality service of the system, as well as advise which kit to buy in order to pump the brakes as efficiently as possible. Remember that your personal safety directly depends on the correct operation of the brake system, therefore, it is not recommended to save on its maintenance.
Hydraulic bike brake system
Technological progress applies to all vehicles, and their two-wheeled representatives are no exception. Instead of the usual cable brakes, improved models that work on hydraulics have come. The principle of operation of such a system is fundamentally different from the mechanical one, here the force from the handle to the pads is transmitted through the brake fluid circulating in the hydraulic line. With an increase in the quality characteristics of brakes, the cost of their maintenance also increases, this should be taken into account when buying a new bike.
Signs indicating the need to bleed hydraulics
There are several indicators that indicate the need for servicing the hydraulic system, among them:
- the brake lever moves too freely or falls through, and the pads react poorly to its pressing or do not work at all;
- the brake lever continues to move smoothly after a sharp push and release of the hand.
How to bleed MTB brakes
Also, system maintenance is necessary if the brake fluid has not been changed for a long time. When replacing components or the entire hydraulic line, its pumping is automatically carried out. Leading brands such as Shimano or Magura use fluids of a specific color and bleed when discolored. Timely maintenance allows you to get the most out of your bike and keeps the cyclist safe on any stretch of the road.
Bleeding Shimano Hydraulic Brakes
Bleeding the brake system using the example of Shimano BR-M640 Zee brakes
Bleeding the hydraulic brake system using the example of Shimano BR-M640 Zee brakes. Also, this method can be used to bleed other models of Shimano brakes, which have the ability to bleed using a special tool Oil Stopper funnel, this method is very simple and does not require special skills.
To bleed the brake, we need:
- Shimano mineral oil;
- Funnel for pumping Oil Stopper;
- A syringe and a transparent tube (any pharmacy will do);
- 7mm box or open-end wrench;
- Hexagon set;
- Paper towels and degreaser (isopropyl alcohol will also work).
(We recommend purchasing a ready-made bleeding kit, it is called the Shimano hydraulic brake bleeding kit).
Use paper towels, as it is very easy to stain parts of the bike when working with brake fluid, which can easily get onto the brake discs and pads.
Before bleeding, it is necessary to remove the wheel with the brake disc. First you need to reset the switch to the smallest star on the cassette. Do this with extreme caution, as the brake rotor can be easily bent.
We remove the pads from the brake caliper so as not to accidentally fill them with mineral oil. It is very important, after we have removed the pads, insert a plug (you can use old pads or a spacer of a suitable size), install it between the pistons to exclude their movement, otherwise, during pumping, the pistons may converge in the brake caliper.
(remove the pads) (install the spacer between the pistons)
Install the brake lever parallel to the ground, unscrew the expansion barrel bolt and screw in the funnel (Shimano Oil Stopper).
(unscrew the expansion tank bolt and screw in the funnel)
We draw mineral oil into the syringe (15-20 ml is enough) and get rid of air bubbles.
(IMPORTANT! Eliminate air from the syringe and tube)
We put the syringe tube on the caliper bleed fitting. Using a 7 mm wrench, open the bleed nipple, counterclockwise (turn is enough)
(we connect the syringe to the caliper through the pumping union)
We press on the syringe (for the rear brake, 15-20 ml is enough to completely pump the system)
(using the key, open the fitting and start pumping)
We close the pumping union, in a reverse motion, without applying much effort (1-2Nm is enough)
(upon completion of pumping, close the fitting)
Unscrew the funnel from the brake lever.
(insert the funnel piston to exclude spillage of mineral oil)
(we unscrew the funnel, screw back the expansion tank cap bolt)
We tighten the bolt for pumping in the expansion tank, do not tighten it tightly (1Nm is enough)
Next, degrease the caliper and brake lever if they get brake fluid.
Insert the pads, place the wheel in the dropouts.
We check that the brake works, and when the brake is pressed, the brake lever does not fall through until the grips.
If the above signs are not observed, then you did everything right, congratulations! (the rear brake has a slight wrinkle compared to the front. this is normal).